Senators said after a classified briefing Wednesday that they were shown a "proof of life" video showing Sgt. Bowe Bergdahl in poor physical condition and believed it helped spur President Barack Obama's decision to swap five Taliban detainees for his release.

But many senators said they continue to have questions about Bergdahl's conduct, as well as the potential for the Taliban officials to return to fight the United States.

"This thing really goes belly up for the president if one of these guys attacks the United States or kills an American," said Sen. Mark S. Kirk, R-Ill. "I think Congress should really tighten up on any transfers out of Gitmo. Gitmo in my view should be a black hole of terrorism that you go to and you never come out of.

"I think they violated the [notification] law because they knew Congress would object and wisely in my view," Kirk said, referring to a requirement that the president notify Congress 30 days before any prisoner transfers — a requirement Obama ignored.

Some senators suggested the health of Bergdahl was a factor.

“All I can say is that his condition in the video made it clear that this man was not in good condition,” said Senate Minority Whip Richard J. Durbin, D-Ill. “This was a proof of life video, which we insisted on before the negotiations commenced, and once having seen it, as we saw it, I am sure there was great concern about his condition. “I think it was a very hard decision,” Durbin continued. “If I had been challenged to make it myself, I might have come to the same conclusion under the pressure of the moment. But now that you can step back and reflect on it it’s easy to pick it apart and criticize it."

The classified briefing was given by officials from the Department of Defense and the State Department.

Kirk agreed that Bergdahl looked ill and that it may have moved Obama — a possible ploy by the Taliban, he surmised.

"He did look like he had deteriorated health-wise," Kirk said. "I think it probably had an emotional impact on the president, which is what the Taliban probably intended."

But he acknowledged that it would be difficult not to feel for Bergdahl.

"Had I been the man actually in charge ... I would have had an emotional reaction getting that video," Kirk said.

Sen. Joe Manchin III, D-W.Va., sounded skeptical.

"The health was deteriorating at the time," he said. "His health was not the critical factor right now. In that one video you could tell he'd been drugged, that was back in December."

Both Republicans and some Democrats have been critical of Obama for not notifying them of the matter, as required by law, and have voiced reservations that the five prisoners who were traded for Bergdahl would return to the fight against the United States.

"I don’t feel assured that these five Taliban detainees, who are high level, will not get back into the fight against us and our allies," said Sen. Kelly Ayotte, R-N.H., upon leaving the briefing.

Kirk noted that the mood in the briefing was somewhat tense and that many left with more questions than answers.

"I think the mood was [that] this has turned pretty negative for the president," Kirk said. "Now that we are learning more and hearing from the actual soldiers that served with Bowe Bergdahl, this has not turned out the way that the president had wanted."

Some of his fellow soldiers have charged that Bergdahl walked off base in a way that indicated he was not coming back, and the Taliban subsequently captured him.

Kirk said it matters if he was a deserter given that the subsequent search for him resulted in the deaths of some of the soldiers involved in the search.

"I think for the American people they would be really in to paying a pretty high price for someone who is a combat veteran," Kirk said. "If the guy was just a deserter they would not be in to paying a very high price for getting him back."

Kirk said the question on whether Bergdahl was a deserter was asked, "and they kind of ducked it."

"I wasn't satisfied with the response," Kirk said. "The vice admiral who answered that question said, 'We are looking into that' and I think a lot of us would be pretty OK with the military justice system looking into that."

Manchin also said that whether Bergdahl shirked his duty remains one of several questions that should be answered.

“We all agree that we are not dealing with a war hero, we are dealing with a soldier that should be looked at more extensively,” Manchin said.